1. Field of the Invention
The present invention relates to a method for remediating contaminated soil, and more particularly, to a method for remediating arsenic-contaminated soil by separating arsenic from arsenic-contaminated soil and treating the separated arsenic.
2. Description of Related Art
Soil contamination results from various causes, including waste dumping, hazardous chemical leakage, the use of agricultural chemicals and fertilizers, and incineration. Soil contamination not only causes various problems, including the disturbance of the soil ecosystem, the contamination of crops, and the absorption of contaminants into the human body, but also acts as a contamination source that causes secondary contamination of surface water, underground water and the atmosphere. Also, soil contamination is more chronic than air and water pollution, and thus requires much time and cost for remediation.
In Korea, the Soil Environment Conservation Act was established and became effective on the basis of recognition of adverse effects of soil contamination on humans and the ecosystem. In the Soil Environment Conservation Act, criteria for 16 items (Cd, Cu, As, Hg, Pb, Cr6+, Zn, Ni, F, organic phosphorus compounds, CN, BTEX, TPH, TCE, and PCE) are established and controlled.
Soil contaminated with arsenic among the above 16 items has been remediated by various processes, including solidification, and stabilization by microorganisms and chemicals. In the solidification and stabilization processes, arsenic present in soil is modified into a form of low toxicity and mobility.
In Korea, an arsenic extraction method that uses 1 N HCl was used to measure the degree of arsenic contamination, but was replaced by an extraction method, which uses aqua regia, according to the revision of the Soil Contamination Process Test Method revised in 2009. Namely, in the existing extraction method that uses 1 N HCl, an arsenic type of high in vivo toxicity is mainly extracted, and whether or not the amount of arsenic extracted exceeds the criterion is determined. However, in the new extraction method using aqua regia, all types of arsenic present in soil are extracted, and whether or not the amount of arsenic extracted exceeds the criterion is determined. Thus, when the contaminated soil is remediated using the existing stabilization and solidification process, it is difficult to satisfy the criterion if the newly revised the Soil Contamination Process Test Method is applied. Namely, in the existing stabilization process, the removal rate of arsenic from soil is low, and thus when arsenic is extracted from the remediated soil, a large amount of arsenic is extracted.
Meanwhile, when a washing process using an acidic solution is applied to soil contaminated with arsenic, arsenic in a relatively unstable form (a water-soluble form, an adsorbed form or a carbonate form) can be extracted, but the extraction of arsenic in a relatively stable crystalline iron oxide form or residual form is limited.
Also, in washing of arsenic-contaminated soil with an acidic solution, there are frequent cases in which released arsenic ions are adsorbed to positively charged iron oxide in an acidic environment to increase rather than decrease the degree of contamination.
Namely, when arsenic-contaminated soil is washed with an acidic solution, arsenic that has been co-precipitated with iron oxide or manganese oxide is released while being negatively charged. In this case, because the surface of iron oxide or manganese oxide is positively charged in an acidic environment, the released arsenic ions are adsorbed again to iron oxide or manganese oxide, thus reducing the efficiency of arsenic removal.
Accordingly, it is expected that, when the conventional soil washing process that uses an acidic washing solution is applied to a soil contaminated with a high concentration of arsenic, the remediation of the soil will be difficult to achieve. Therefore, it is required to develop a new process which can overcome the limitation of this conventional process.